The vagina tends to loosen during arousal, so I wouldn't worry much. If it doesn't fit, you could warm up with fingers.
I see you talking a lot about foreplay but you have not mentioned lube at all. Get a good water based lube like KY. I have to use it too. We only have sex about once every 5 or 6 weeks and we have the same issue.
It definitely is tighter
It might feel a little tight at first, but the vagina stretches. I mean, it's designed for a baby to come out of it. Your penis will fit.
Just go slowly, make sure she's lubricated enough - foreplay is always a good idea - and things will be fine. Just listen to her, and if she says it hurts, ask her what she needs to make it not hurt, or if she needs to stop.
I don’t think that would make much difference. Maybe females would care to comment - Ladies, does your vaginal opening feel ‘tighter’ when you haven’t had intercourse for a period of time? I’m thinking maybe it could just slightly, but would pretty quickly return to normal once you resume - ?? Is this assumption off-base or more or less correct?